(1) Field of the Invention
The field of the invention is in the broad sense medical syringes. More specifically, the invention relates to dilatation catheters of the inversion-eversion type and a plunger-type actuator therefor characterized by a small bore stage adapted to provide an initial high fluid pressure to evert the balloon element of the catheter and a subsequent lower pressure, higher volume condition to inflate the balloon element.
(2) Description of the Prior Art
I am not aware of any combined large and small bore syringe suitable for catheter actuation, as described above, or for other purposes requiring an initial high pressure, low volume condition followed by a low pressure, high volume condition.
I am aware of the following prior art which disclose a variety of concentric dual plunger syringes: U.S. Pat. Nos. 2,869,543; 2,929,459; 3,326,215; 3,685,514; 4,128,009; 4,188,949; 4,254,768; 4,273,257.
In the foregoing patents, the plungers are of substantially the same diameter, and the purpose of the dual syringe arrangement is either to mix two different fluids during the course of injection or to maintain the fluids in separate condition.